PC2100/ 3200

I just checked on Crucial for Ram for my ASRock K7VM2 Mobo.Mobo manual says PC133 or PC2100. Crucial say I can use PC3200- its cheaper, for some strange reason! However, its CL speed is 3, as opposed to 2.5 on the PC2100. Apparently, the smaller number is faster- but how much faster? Would I notice the difference? I dont do gaming or anything, & am on a pension, so cost is important! Any advise, Please?